Single unit activity in the auditory cortex and the medial geniculate body of the rhesus monkey: behavioral...

Three Rhesus monkeys were trained to respond to a given auditory signal, the nature of which could be predicted from a preceding visual stimulus. The activity of 28 units in the auditory cortex and 53 units in the Medial Geniculate Body (MGB) of the monkey was recorded during task-performance conditions, as well as in the non-performance conditions. The activity of about one third of the cortical and MGB units was independent of the behaving status of the animal. In other units, the response to an auditory signal delivered during task-performance conditions as compared to the response recorded during non-performance periods was either augmented or attenuated. Furthermore, it was found that the spontaneous activity of most of the MGB and cortical units was continuously affected by either an excitatory or an inhibitory input, activated by the behavioral state. The temporal characteristics of behavioral modulation were studied by computing an amplification curve for all MGB units characterized by a 'through stimulus excitation' type of response. Analysis of these curves together with the behavioral effect on the spontaneous activity allows the suggestion of possible mechanisms by which the behavioral state of the monkey modulates the activity in the thalamocortical segment of the auditory system.